Smaller size and weight factor greatly into user selection for many handheld, head-mounted, or airborne imaging systems, even when the added weight or size can provide otherwise useful capabilities. The conventional means for field of view (FOV) switching generally requires more elements and/or longer optical paths over equivalent fixed FOV systems. As reconfigurable optic technologies are becoming more mature, switchable optic elements integrated with static optics can provide FOV switching capability in a smaller size and weight than a conventional zoom system. A variety of reconfigurable lenses are discussed in literature. Ye, et al. (2004) and Li, et al. (2010) give examples of two different types of Liquid Crystal (LC) lenses that vary the radial index profile of the LC material by changing the voltage across different electrode configurations. See, Ye et al., “Liquid-crystal lens with a focal length that is variable in a wide range.” Applied Optics, Vol. 43, No. 35, pp. 6407-6412 (2004). See, also, Li et al., “Liquid crystal lenses: Liquid crystals promise compact lenses with variable focus.” Laser Focus World, December 2010, accessible online. As long as the effects of diffraction are small, color dispersion is expected to be similar to that experienced by a conventional lens of the same optical power. Liquid Crystal Diffractive Lenses (LCDLs) are discussed in Valley, et al. (2010) and U.S. Pat. No. 5,751,471 to Chen, et al (1998). See, Valley et al., “Nonmechanical bifocal zoom telescope,” Optics Letters, Vol. 35, No. 15, pp. 2582-2584 (2010). See, also, U.S. Pat. No. 5,751,471, entitled, “Switchable lens and method of making,” issued May 12, 1998 to Chen et al. The color dispersion in LCDLs is much more pronounced.
Bagwell, et al. (2005 and 2006) describe several LC and non-LC reconfigurable elements assembled into non-mechanical zoom configurations, including one employing Liquid Crystal Diffractive Lenses (LCDLs). See, Bagwell et al., “Adaptive Optical Zoom Sensor,” Sandia Report SAND2005-7208, Sandia National Laboratories, November 2005. See, also, Bagwell et al., “Liquid crystal based active optics,” Proc. SPIE 6289, Novel Optical Systems Design and Optimization IX, 628908-1 (2006). From the above cited literature, two main challenges exist when integrating LCDLs into a zoom system, namely large color dispersion and sensor illumination changes with FOV.